The field of the disclosure relates generally to direct current (DC) converters and, more particularly, to modified droop control of DC converters and methods of use.
Many known electrical power applications utilize parallel power sources, or redundant power sources, to share an electrical load. Parallel power sources improve reliability for the overall electrical power system by dynamically controlling power output as loads and power sources are connected and disconnected. Such applications typically demand a particular range of output voltage from the power sources and, to properly share the electrical load, the output voltages of parallel power sources should be balanced. For example, in an application where the electrical load is shared equally, each parallel power source should have a substantially equal output voltage. Conversely, unequal output voltages result in unequal sharing of the electrical load.
Many known electrical power applications further utilize DC converters to convert alternating current (AC) power to DC, to step-up DC voltages, or to step-down DC voltages to the appropriate range for a DC bus or a DC load. Such DC converters include DC-DC and AC-DC converters. In some electrical power applications, DC converters receive a variable input voltage that demands certain voltage regulation be carried out by the DC converter. One such known DC converter is a variable frequency resonant converter, sometimes referred to as an LLC converter (so called for its use of an inductor-inductor-capacitor power circuit). In a variable frequency resonant converter, the output voltage of the converter is controlled by adjusting a switching frequency of semiconductor devices within the converter.
Generally, parallel variable frequency resonant converters are characterized by droop, which includes a frequency droop component and a voltage droop component. A given converter's droop characteristic governs its real and reactive power output as switching frequency varies. Resonant frequency converters are characterized by a resonant frequency at which the converter achieves peak efficiency. A common control scheme for parallel variable frequency resonant converters is droop control. As the electrical load changes, so too does the demanded power. In a droop control scheme, the switching frequency is adjusted based on the power output to maintain an output voltage setpoint. Consequently, the efficiency of the variable frequency resonant converter varies accordingly.